Method for preparing a polymeric composition

ABSTRACT

A method for preparing a polymeric composition in which an inorganic compound is firmly consolidated in an organic polymer, which comprises polymerizing at least one radical polymerizable vinyl monomer in an aqueous medium polymerization system comprising an inorganic compound dispersed in the presence of an organic acid monomer or organic acid salt monomer, by using a radical polymerization initiator.

This is a division, of application Ser. No. 06/898,496, filed Aug. 21,1986 now U.S. Pat. No. 4,783,501.

The present invention relates to a novel method for preparing apolymeric composition in which an inorganic compound is firmlyconsolidated in an organic polymer.

Heretofore, there have been active researches for the development ofcomposite materials, wherein two or more materials are combined tomutually complement the properties of the respective materials topresent a new useful function. In recent years, an attention has beendrawn not only to mere application of an inorganic compound powder to acomposite material as a filler, but also to a composite material such asa ceramic material, a magnetic material or a dental material, wherein apowder of an inorganic compound having a high level of function impartedthereto is combined with an organic polymer. However, in this case, thematerials to be combined are mutually substantially different in theirproperties, and the interfacial affinity such as the compatibility oradhesion is poor. Thus, such a combination has inherent drawbacks suchthat the effectiveness of the combination can not adequately beimproved, and the function of the inorganic compound powder itself canhardly adequately be utilized.

Various methods for modifying the surface properties of a powder havebeen proposed to overcome these drawbacks, to improve the interfacialaffinity of the inorganic compound with the organic polymer substanceand to attain high packing density, uniform dispersion and highstrength. For instance, there may be mentioned a mechano-chemical methodin which an inorganic compound is pulverized in the presence of areactive monomer, followed by grafting an organic polymer, or aradiation method wherein an inorganic substance is irradiated with ahigh-energy radiation to be grafted with an organic polymer. Thesemethods, however, require a grinding step or installation of a radiationequipment, resulting in complication of the manufacturing process andincrease of the manufacturing cost, and present difficult problems forthe practicability of the process.

Further, as an example for the surface modification of a powder in whichan in situ polymerization for microcapsulation is employed, the presentinventors have previously proposed a method for firmly consolidating aninorganic compound and an organic polymer, wherein a radicalpolymerizable vinyl monomer and an inorganic compound as a thirdcomponent are contacted in the presence of a certain specific organicacid monomer or organic acid salt monomer (U.S. Pat. No. 4,435,540,issued on Mar. 6, 1984). However, this method is based on thenon-catalytic polymerization of the vinyl monomer by the contact of thespecific organic acid monomer or organic acid salt monomer with theinorganic compound, and thus has a problem that the degree ofpolymerization of the monomer and the graft rate i.e. the ratio of theorganic polymer firmly consolidated to the formed polymer, are notnecessarily adequate. Further, the applicable vinyl monomer isrestricted to the one composed mainly of methyl acrylate or methylmethacrylate, and thus has a drawback that the useful monomer is ratherlimited.

It is an object of the present invention to provide a polymericcomposition in which an organic polymer is uniformly and firmly bondedto the surface of an inorganic compound with a remarkably high degree ofpolymerization and graft rate.

The present invention provides a method for preparing a polymericcomposition in which an inorganic compound is firmly consolidated in anorganic polymer, which comprises polymerizing at least one radicalpolymerizable vinyl monomer in an aqueous medium polymerization systemcomprising an inorganic compound dispersed in the presence of an organicacid monomer or organic acid salt monomer, by using a radicalpolymerization initiator.

Now, the present invention will be described in detail with reference tothe preferred embodiments.

The organic acid monomer or organic acid salt monomer is preferably asulfonic acid monomer or sulfonate monomer of the formula: ##STR1##wherein R₁ is a hydrogen atom, a C₁ -C₂₀ alkyl group or a halogen atom,X is --CONH--, ##STR2## (wherein each of R₂ and R₃ is a hydrogen atom ora C₁ -C₁₅ alkyl group, and R₄ is a C₁ -C₁₅ alkylene group),--COO(CH_(2m) (wherein m is an integer of 1 to 20) or CH_(2n) (wherein nis an integer of 0 to 20), and Y is a hydrogen atom, an ammonium radicalor an alkali metal atom; or a carboxylic acid monomer or carboxylatemonomer of the formula: ##STR3## wherein each of R₅ and R₆ is a hydrogenatom, a C₁ -C₁₅ alkyl group or --COOA (wherein A is a hydrogen atom, anammonium radical or an alkali metal atom), R₇ is a hydrogen atom or a C₁-C₁₅ alkyl group, Z is a hydrogen atom, an ammonium radical or an alkalimetal atom, and each of R₈ and R₉ is a hydrogen atom or a C₁ -C₁₅ alkylgroup.

A feature of the present invention is that the interaction between thesurface of the inorganic compound and the polymer formed according tothe method of the present invention, is derived from a firmlyconsolidated chemical bond beyond simple adsorption or physical adhesionby e.g. van der Waals adsorption.

Referring to a specific manner for carrying out the present invention,an inorganic compound is suspended and dispersed in an aqueous medium ata temperature within a range in which a radical polymerization initiatordecomposes, and an organic vinyl monomer, a specific organic acidmonomer or organic acid salt monomer and a radical polymerizationinitiator are added and stirred to conduct aqueous heterogeneouspolymerization, whereupon a copolymer of the vinyl monomer with theorganic acid monomer or organic acid salt monomer is uniformly andfirmly bonded to the surface of the inorganic compound with a highdegree of polymerization and graft rate in a predetermined period ofpolymerization.

In this case, if a usual dispersant such as a polyanion is used, theeffect of the present invention can not be obtained.

The sulfonic acid monomer or sulfonate monomer of the formula I isrequired to have a double bond as an active site attributable to thepolymerizability by a radical polymerization initiator and a sulfonicacid group as an active site which brings about a firm consolidation bythe interaction with hydroxyl groups present on the surface of theinorganic compound and the resulting polymer. Any compound having astructure containing these functional groups can be employed. Forinstance, there may be employed 2-acrylamido-2-methylpropanesulfonicacid (hereinafter referred to simply as AMS), sodium2-methacryloylethanesulfonate (hereinafter referred to simply asSEM-Na), sodium 3-methacryloylpropanesulfonate (hereinafter referred tosimply as SPS), sodium 2-propenesulfonate (hereinafter referred tosimply as NaAS) and sodium 2-methyl-2-propenesulfonate (hereinafterreferred to simply as NaMS). Among them, particularly preferred are AMScontaining an amide linkage and SEM-Na and SPS containing an esterlinkage, as they have high polymerization activities and graftefficiency (i.e. efficiency for firm consolidation of the formedpolymer).

The carboxylic acid monomer or carboxylate monomer of the formulas IIand III, is required to have a double bond as an active siteattributable to the polymerizability by a radical polymerizationinitiator and a carboxylic acid group as an active site which bringsabout a firm consolidation by the interaction with hydroxyl groupspresent on the surface of the organic compound and the formed polymer.Any compound having a structure containing these functional groups maybe employed. For instance, there may be mentioned acrylic acid,methacrylic acid, crotonic acid, tiglic acid, cinnamic acid, maleicanhydride and citraconic anhydride. Among them, particularly preferredare acrylic acid, methacrylic acid, crotonic acid and maleic anhydride,as they have high polymerization activities and graft efficiency (i.e.efficiency for firm consolidation of the formed polymer).

As the inorganic compound to be used in the present invention, acarbide, nitride or boride of silicon or zirconium, or zirconium oxideis particularly preferred, in view of remarkable effects for theactivation of the vinyl monomer and for the firm consolidation with thepolymer.

As the vinyl monomer to be used in the present invention, anyconventional radical polymerizable vinyl monomer may be employed.

As the radical polymerization initiator to be used in the presentinvention, any conventional peroxide or azo compound may be employed.However, a radical polymerization initiator which is decomposable at atemperature within a range of from 40° to 100° C. is particularlyuseful. Among them, particularly preferred from the viewpoint of thegraft rate are peroxides such as benzoyl peroxide,azobisisobutyronitrile and potassium persulfate, and azo compounds. Now,the present invention will be described in further detail with referenceto Examples. However, it should be understood that the present inventionis by no means restricted by these specific Examples. In the Examplesand Comparative Examples, the term "parts" means "parts by weight"unless otherwise specified.

EXAMPLE 1 and COMPARATIVE EXAMPLES 1 to 5

In a 1000 ml four-necked flask equipped with a condensor, a nitrogeninlet, a stirrer and a thermocouple for detecting the internaltemperature, 270.0 g of silicon nitride, used as the inorganic compound,was suspended in 700 ml of deionized water to form a dispersion. Afterflushing the flask with nitrogen for 30 minutes, 28.0 g of methylmethacrylate, used as the vinyl monomer, was added to the dispersionwith vigorous stirring under a nitrogen stream. Then, the above reactionmixture was heated to 70° C. in a warm water bath. After confirming theuniform dispersion of the added monomer, a solution of 10.0 g of SEM-Naas the sulfonate monomer in 20 ml of deionized water and a solution of1.0 g of benzoyl peroxide as the radical initiator in 2.0 g of methylmethacrylate, were gradually added thereto. The mixture was reacted forpolymerization at the same temperature for 8 hours. After completion ofthe polymerization, about 5 g of the reaction mixture was sampled. Thesample was tested for the amount of the remaining unreacted monomer bygas chromatography using dioxane as internal standard, and theconversion was obtained.

Further, the polymeric composition after the reaction was thoroughlydried at 105° C. for one day and night, and then about 5 g of thecomposition was completely burned at 650° C. for 3 hours, whereupon theamount of the polymer consolidated to the inorganic compound wascalculated from the weight reduction. Then, the consolidation rate wasobtained in accordance with the following formula: ##EQU1##

For the purpose of comparison, similar polymerization operation andevaluation after the polymerization were conducted with respect to thepolymerization behavior in the cases where the radical initiator wasomitted as in the conventional non-catalytic polymerization system, thesulfonic acid monomer or sulfonate monomer was not added, and adispersant was added. The results are shown in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                Radical                                                                       polymeri- Inorganic                                                      Sulfonate                                                                          zation                                                                             Vinyl                                                                              compound                                                       monomer                                                                            initiator                                                                          monomer                                                                            Silicon                                                                             Dispersant                                                                            Deionized                                                                           Conversion                                                                          Consolida-                           SEM-Na                                                                             BPO  MMA  nitride                                                                             Sodium hexa-                                                                          water of monomer                                                                          tion rate                            (parts)*1                                                                          (parts)                                                                            (parts)                                                                            (parts)*2                                                                           metaphosphate                                                                         (parts)                                                                             (%)   (%)*3                         __________________________________________________________________________    Example 1                                                                            10.0 1.0  30.0 270.0 --      720   -100  96                            Comparative                                                                          10.0 --   30.0 270.0 --      720   71    88                            Example 1                                                                     Comparative                                                                          --   1.0  30.0 270.0 --      720   90     4                            Example 2                                                                     Comparative                                                                          10.0 1.0  30.0 270.0 3.0     720   95    45                            Example 3                                                                     __________________________________________________________________________     *1: CH.sub.2C.CH.sub.3COOC.sub.2 H.sub.4SO.sub.3 Na                           *2: Special grade reagent                                                     ##STR4##                                                                      BPO: Benzoyl peroxide, MMA: Methyl methacrylate                          

It is evident from Table 1 that in the system of Comparative Example 2wherein no sulfonic acid monomer or sulfonate monomer was added, theconsolidation rate was very poor although a high conversion wasobtainable, and a tendency for the separation of the inorganic compoundand the homopolymer was observed. Further, it is evident that ascompared with Comparative Example 1, the method of the present invention(Example 1) wherein a radical polymerization initiator was added, issuperior in both the conversion of monomer and the consolidation rate.Further, in the system of Comparative Example 3 wherein a dispersant wasadded, the consolidation rate was substantially low, and a tendency forthe separation of the homopolymer was observed as in the case ofComparative Example 2.

The polymeric compositions of Example 1 and Comparative Examples 1 to 3as shown in Table 1, were continuously extracted by Soxhlet for 50 hourswith benzene, 50 hours with acetone and 200 hours withdimethylformamide, as good solvents for methyl methacrylate-SEM-Nacopolymers, whereby the reduction in the polymer contents was studied.The results are shown in Table 2. Here, the polymer content after beingthoroughly extracted with dimethylformamide for 200 hours, was evaluatedto be a graft rate in the sense that the polymer is firmly consolidatedto the surface of the inorganic compound by means of a chemical bond.For the purpose of comparison, a similar extraction operation wasconducted with respect to each of compositions (Comparative Examples 4and 5) wherein an inorganic powder (silicon nitride) was coated with apolymer obtained by the solvent blending with polymethyl methacrylate orwith a methyl methacrylate-SEM-Na copolymer whereby the reduction in thepolymer content was compared.

                                      TABLE 2                                     __________________________________________________________________________                     Polymer Polymer content                                             Preparation of                                                                          content after continuous                                            polymeric before  extraction*4                                                                           Graft                                              composition*1                                                                           extraction (%)                                                                        (graft rate) %                                                                         efficiency*5 (%)                            __________________________________________________________________________           Polymerization                                                                system                                                                 Example 1                                                                            Presence of SEM-                                                                        9.6     9.1      90                                                 Na (Present                                                                   invention)                                                             Comparative                                                                          Non-catalytic                                                                           6.5     1.8      23                                          Example 1                                                                            polymerization                                                                system without                                                                addition of BPO                                                        Comparative                                                                          No addition of                                                                          1.1     -0.0     -0                                          Example 2                                                                            SEM-Na as opposed                                                             to Example 1                                                           Comparative                                                                          Addition of                                                                             4.5     0.9      8.6                                         Example 3                                                                            dispersant as                                                                 opposed to                                                                    Example 1                                                                     Blend system                                                           Comparative                                                                          Solvent blend of                                                                        9.6     -0.0     --                                          Example 4                                                                            polymethyl meth-                                                              acrylate*2                                                             Comparative                                                                          Solvent blend of                                                                        9.5     -0.0     --                                          Example 5                                                                            methyl meth-                                                                  acrylate-SEM-Na                                                               copolymer*3                                                            __________________________________________________________________________     *1: Silicon nitride was used as the inorganic compound.                       *2: Acrypet (VH), manufactured by Mitsubishi Rayon Co., Ltd., was used.       *3: A copolymer prepared in the same manner as in Example 1 except that       the method of the present invention was conducted in the absence of the       inorganic compound, was used.                                                 *4: Continuous extraction by Soxhlet for 50 hours with benzene, 50 hours      with acetone and 200 hours with dimethylformamide.                            ##STR5##                                                                 

The polymer components in the compositions of Comparative Examples 2, 4an 5 were completely extracted by the above continuous extractionoperation irrespective of the system being of a polymerization type orof a solvent blend type. This indicates that even in the polymerizationsystem, a polymer forming in the absence of a sulfonic acid monomer orsulfonate monomer, is merely chemically or physically adsorbed on thesurface of the inorganic compound. In Comparative Examples 1 and 3, apart of the formed polymer was firmly consolidated to the inorganiccompound, but the level of the graft rate was very low. Whereas, inExample 1 according to the method of the present invention wherein aradical polymerization initiator was added in the presence of a sulfonicacid monomer or sulfonate monomer, the extracted rate after the seriesof severe extraction operations, was very small, indicating a high graftrate. Further, even when the polymeric composition was subjected towashing treatment with an aqueous NaOH solution, it showed a high graftrate substantially equal to the level after the extraction operations.Thus, it was confirmed that the firm consolidation of the polymer to thesurface of the inorganic compound was attributable to the presence of acovalent bond-type graft linkage as a chemical bond stronger than ahydrogen bond or ionic bond at the interface.

EXAMPLES 2 to 5

The polymerization was carried out in the same manner as in Example 1,except that SPS, AMS, NaAS or NaMS was used as the sulfonic acid monomeror sulfonate monomer instead of SEM-Na. The graft efficiency wasmeasured, and the results are shown in Table 3.

                                      TABLE 3                                     __________________________________________________________________________                                    Inorganic    Graft                                            Radical polymeri-                                                                      Vinyl  compound                                                                             Deionized                                                                           effi-                            Acid       Amounts                                                                            zation initiator                                                                       monomer                                                                              Silicon                                                                              water ciency                           monomer    (parts)                                                                            BPO (parts)                                                                            MMA (parts)                                                                          nitride (parts)                                                                      (parts)                                                                             (%)                              __________________________________________________________________________    Example 1                                                                           SEM-Na                                                                             10.0 1.0      30.0   270.0  720   90                               Example 2                                                                           SPS *1                                                                             10.5 1.0      30.0   270.0  720   92                               Example 3                                                                           AMS *2                                                                             9.9  1.0      30.0   270.0  720   90                               Example 4                                                                           NaAS *3                                                                            6.5  1.0      30.0   270.0  720   75                               Example 5                                                                           NaMS *4                                                                            7.1  1.0      30.0   270.0  720   78                               __________________________________________________________________________     *1: CH.sub.2 ═C.CH.sub.3 --COOC.sub.3 H.sub.6 --SO.sub.3 Na               *2: CH.sub.2 ═CH--CONH--(CCH.sub.3).sub.2 CH.sub.2 SO.sub.3 H             *3: CH.sub.2 ═CHCH.sub.2 SO.sub.3 Na                                      *4: CH.sub.2 ═C.CH.sub.3 --CH.sub.2 SO.sub.3 Na                      

As is apparent from Table 3, the graft efficiency was very high withSEM-Na, SPS and AMS.

EXAMPLES 6 to 9

The reaction was conducted in the same manner as in Example 1 exceptthat the type of the radical polymerization initiator was changed, andthe compositions thereby obtained were evaluated. The results are shownin Table 4.

                                      TABLE 4                                     __________________________________________________________________________                      Acid        Inorganic    Graft                              Radical           monomer                                                                            Vinyl  compound                                                                             Deionized                                                                           effi-                              polymeriza-  Amount                                                                             SEM-Na                                                                             monomer                                                                              Silicon                                                                              water ciency                             tion initiator                                                                             (parts)                                                                            (parts)                                                                            MMA (parts)                                                                          nitride (parts)                                                                      (parts)                                                                             (%)                                __________________________________________________________________________    Example 1                                                                           BPO    1.0  10.0 30.0   270.0  720   90                                 Example 6                                                                           LPO *1 1.0  10.0 30.0   270.0  720   93                                 Example 7                                                                           AIBN *2                                                                              1.0  10.0 30.0   270.0  720   90                                 Example 8                                                                           AIBA *3                                                                              1.0  10.0 30.0   270.0  720   70                                 Example 9                                                                           KPS *4 1.0  10.0 30.0   270.0  720   73                                 __________________________________________________________________________     *1: Lauroyl peroxide                                                          *2: Azobisisobutyronitrile                                                    *3: 2,2'-Azobis(2aminodipropane)hydrochloride                                 *4: Potassium persulfate                                                 

As is apparent from Table 4, the graft efficiency is higher withlipophilic radical polymerization initiators such as BPO, LPO and AIBNthan with water-soluble AIBA and KPS.

EXAMPLES 10 and 11

the reaction was conducted in the same manner as in Example 1 exceptthat the vinyl monomer identified in Table 5 was used instead of methylmethacrylate as the vinyl monomer, and the compositions thereby obtainedwere evaluated. The results are shown in Table 5.

                                      TABLE 5                                     __________________________________________________________________________                    Acid          Inorganic    Graft                                              monomer                                                                            Radical polymeri-                                                                      compound                                                                             Deionized                                                                           effi-                              Vinyl      Amount                                                                             SEM-Na                                                                             zation   Silicon                                                                              water ciency                             monomer    (parts)                                                                            (parts)                                                                            BPO (parts)                                                                            nitride (parts)                                                                      (parts)                                                                             (%)                                __________________________________________________________________________    Example 1                                                                           MMA  30.0 10.0 1.0      270.0  720   90                                 Example 10                                                                          ST   30.0 10.0 1.0      270.0  720   76                                 Example 11                                                                          AN   30.0 10.0 1.0      270.0  720   74                                 __________________________________________________________________________     MMA: Methyl methacrylate, ST: Styrene, AN: Acrylonitrile                 

As is apparent from Table 5, according to the method of the presentinvention, a high graft efficiency can be attained with either one ofthe vinyl monomers (Examples 10 and 11).

EXAMPLE 12

The reaction was conducted in the same manner as in Example 1 exceptthat the type of the inorganic compound was changed, and the compositionthereby obtained was evaluated. The results are shown in Table 6.

                                      TABLE 6                                     __________________________________________________________________________                     Acid Radical Vinyl      Graft                                                 monomer                                                                            polymerization                                                                        monomer                                                                            Deionized                                                                           effi-                                Inorganic   Amount                                                                             SEM-Na                                                                             BPO     NMA  water ciency                               compound    (parts)                                                                            (parts)                                                                            (parts) (parts)                                                                            (parts)                                                                             (%)                                  __________________________________________________________________________    Example 1                                                                           Silicon                                                                             270.0                                                                              10.0 1.0     30.0 720   92                                         carbide                                                                 Example 2                                                                           Zirconium                                                                           270.0                                                                              10.0 1.0     30.0 720   93                                         oxide                                                                   Example 3                                                                           Zirconium                                                                           270.0                                                                              10.0 1.0     30.0 720   94                                         nitride                                                                 Example 4                                                                           Zirconium                                                                           270.0                                                                              10.0 1.0     30.0 720   91                                         boride                                                                  Example 5                                                                           Zirconium                                                                           270.0                                                                              10.0 1.0     30.0 720   90                                         carbide                                                                 __________________________________________________________________________

As is apparent from Table 6, the method of the present invention issuperior to the conventional non-catalytic polymerization system in boththe polymerization degree and the graft efficiency, and thus indicatesthat it is capable of providing a polymeric composition of a higherquality.

EXAMPLE 13 and COMPARATIVE EXAMPLES 6 to 9

As an evaluation of the applicability of the polymeric compositionobtained by the method of the present invention to a composite material,a combination of the polymeric composition with polymethyl methacrylateas matrix (inorganic compound content: 80 wt. %) was press-molded at200° C. under 20 kg/cm², and the molded product was evaluated for theouter appearance and bending strength. The results are shown in Table 7.

                                      TABLE 7                                     __________________________________________________________________________                            Composite material                                                            composition *1                                                                           Outer                                                         Polymer                                                                            Polymeric  appearance                                                                          Bending                                     Polymeric   content                                                                            composition                                                                         PMMA of molded                                                                           strength                                    composition (%)  (parts)                                                                             (parts)                                                                            product                                                                             (kg/cm.sup.2)                        __________________________________________________________________________    Example 13                                                                           Example 1   9.6  88    12   ⊚                                                                    283                                         Present invention                                                      Comparative                                                                          Comparative Example 1                                                                     6.5  86    14   Δ                                                                             190                                  Example 6                                                                            Non-catalytic                                                                 polymerization                                                                system without                                                                addition of BPO                                                        Comparative                                                                          Comparative Example 2                                                                     1.1  81    19   X     72                                   Example 7                                                                            No addition of                                                                SEM-Na as opposed                                                             to Example 1                                                           Comparative                                                                          Comparative Example 3                                                                     4.5  84    16   Δ                                                                             140                                  Example 8                                                                            Addition of                                                                   dispersant as opposed                                                         to Example 1                                                           Comparative                                                                          Non-treated silicon                                                                       --   80    20         64                                   Example 9                                                                            nitride                                                                __________________________________________________________________________     *1: The ratio of inorganic compound/organic compound = 80/20.                 PMMA: Polymethyl methacrylate, Acrypet (VH), manufactured by Mitsubishi       Rayon Co., Ltd.                                                               ⊚: Good,                                                       Δ: Fair,                                                                X: Poor,                                                                       : Bad                                                                   

As is apparent from Table 7, according to the method of the presentinvention (Example 13), a sustantial improvement in the effects of thecombination is observed with respect to the outer appearance andstrength of the molded product.

EXAMPLE 14 and COMPARATIVE EXAMPLES 10 to 14

The polymerization and evaluation were conducted in the same manner asin Example 1 except that methacrylic acid as a carboxylic acid monomerwas used instead of the sulfonate monomer. For the purpose ofcomparison, similar polymerization operation and evaluation after thepolymerization were conducted with respect to the polymerizationbehavior in the cases where no radical polymerization initiator wasadded as in the conventional non-catalytic polymerization system, nocarboxylic acid monomer was added, and a dispersant was added. Theresults are shown in Table 8.

                                      TABLE 8                                     __________________________________________________________________________           Carboxylic                                                                          Radical                                                                 acid  polymeri- Inorganic                                                     monomer                                                                             zation                                                                             Vinyl                                                                              compound                                                                           Dispersant                                               Methyl                                                                              initiator                                                                          monomer                                                                            Silicon                                                                            Sodium hexa-                                                                          Deionized                                                                           Conversion                                 methacrylic                                                                         BPO  MMA  nitride                                                                            metaphosphate                                                                         water of monomer                                                                          Consolidation                        acid*1                                                                              (parts)                                                                            (parts)                                                                            (parts)*2                                                                          (parts) (parts)                                                                             (%)   rate (%)*3                    __________________________________________________________________________    Example 14                                                                           10.0  1.0  30.0 270.0                                                                              --      720   -100  98                            Comparative                                                                          10.0  --   30.0 270.0                                                                              --      720   73    90                            Example 10                                                                    Comparative                                                                          --    1.0  30.0 270.0                                                                              --      720   90     5                            Example 11                                                                    Comparative                                                                          10.0  1.0  30.0 270.0                                                                              3.0     720   93    41                            Example 12                                                                    __________________________________________________________________________     *1: CH.sub.2C(CH.sub.3)COOH                                                   *2: Special grade reagent                                                     ##STR6##                                                                      BPO: Benzoyl peroxide, MMA: Methyl methacrylate                          

It is evident from Table 8 that in the system where no carboxylic acidmonomer was added as in Comparative Example 11, the consolidation ratewas very low although the conversion was high, and a tendency forseparation of the inorganic compound and the homopolymer was observed.It was further evident that as compared with Comparative Example 10, themethod of the present invention is superior in both the conversion ofmonomer and the consolidation rate. Further, in the system ofComparative Example 12 wherein a dispersant was added, the consolidationrate was substantially low, and a tendency for the separation of thehomopolymer was observed as in the case of Comparative Example 11.

The polymeric compositions of Example 14 and Comparative Examples 10 to12 as shown in Table 8, were continuously extracted by Soxhlet for 50hours with benzene, 50 hours with acetone and 200 hours withdimethylformamide, as good solvents for methyl methacrylate-methacrylicacid copolymers, whereby the reduction in the polymer contents wasstudied. The results are shown in Table 9. Here, the polymer contentafter being thoroughly extracted with dimethylformamide for 200 hours,was evaluated to be a graft rate in the sense that the polymer is firmlyconsolidated to the surface of the inorganic compound by means of achemical bond. For the purpose of comparison, a similar extractionoperation was conducted with respect to each of compositions(Comparative Examples 13 and 14) wherein an inorganic powder (siliconnitride) was coated, with a polymer obtained by the solvent blendingwith polymethyl methacrylate or with a methyl methacrylate-methacrylicacid copolymer whereby the reduction in the polymer content wascompared.

                                      TABLE 9                                     __________________________________________________________________________                     Polymer Polymer content                                             Preparation of                                                                          content after continuous                                            polymeric before  extraction*4                                                                           Graft                                              composition*1                                                                           extraction (%)                                                                        (graft rate) %                                                                         efficiency*5 (%)                            __________________________________________________________________________           Polymerization                                                                system                                                                 Example 14                                                                           Presence of                                                                             9.7     9.2      92                                                 methacrylic acid                                                              (present invention)                                                    Comparative                                                                          Non-catalytic                                                                           6.9     2.0      26                                          Example 10                                                                           polymerization                                                                system without                                                                addition of BPO                                                        Comparative                                                                          No addition of                                                                          1.1     -0.0     -0                                          Example 11                                                                           methacrylic acid                                                              as opposed to                                                                 Example 14                                                             Comparative                                                                          Addition of                                                                             4.1     0.7      6.8                                         Example 12                                                                           dispersant as                                                                 opposed to                                                                    Example 14                                                                    Blend system                                                           Comparative                                                                          Solvent blend of                                                                        9.5     -0.0     --                                          Example 13                                                                           polymethyl meth-                                                              acrylate*2                                                             Comparative                                                                          Solvent blend of                                                                        9.6     -0.0     --                                          Example 14                                                                           methyl meth-                                                                  acrylate-methyl                                                               methacrylic acid                                                              copolymer*3                                                            __________________________________________________________________________     *1: Silicon nitride was used as the inorganic compound.                       *2: Acrypet (VH), manufactured by Mitsubishi Rayon Co., Ltd., was used.       *3: A copolymer prepared in the same manner as in Example 14 except that      the method of the present invention was conducted in the absence of the       inorganic compound, was used.                                                 *4: Continuous extraction by Soxhlet for 50 hours with benzene, 50 hours      with acetone and 200 hours with dimethylformamide.                            ##STR7##                                                                 

The polymer components in the compositions of Comparative Examples 11,13 and 14 were completely extracted by the above continuous extractionoperation irrespective of the system being of a polymerization type orof a solvent blend type. This indicates that even in the polymerizationsystem, a polymer forming in the absence of a carboxylic acid monomer,is merely chemically or physically adsorbed on the surface of theinorganic compound. In Comparative Examples 10 and 12, a part of theformed polymer was firmly consolidated to the inorganic compound, butthe level of the graft rate was very low. Whereas, in Example 14according to the method of the present invention wherein a radicalpolymerization initiator was added in the presence of a carboxylic acidmonomer, the extracted rate after the series of severe extractionoperations, was very small, indicating a high graft rate. Further, evenwhen the polymeric composition was subjected to washing treatment withan aqueous NaOH solution, it showed a high graft rate substantiallyequal to the level after the extraction operations. Thus, it wasconfirmed that the firm consolidation of the polymer to the surface ofthe inorganic compound was attributable to the presence of a covalentbond-type graft linkage as a chemical bond stronger than a hydrogen bondor ionic bond at the interface.

EXAMPLES 15 to 19

The polymerization was carried out in the same manner as in Example 14,except that acrylic acid, crotonic acid, tiglic acid, cinnamic acid ormaleic anhydride was used as the carboxylic acid monomer instead ofmethacrylic acid. The graft efficiency was measured, and the results areshown in Table 10.

                                      TABLE 10                                    __________________________________________________________________________                                       Inorganic                                                     Radical polymeri-                                                                      Vinyl  compound                                                                             Deionized                           Carboxylic    Amount                                                                             zation initiator                                                                       monomer                                                                              Silicon                                                                              water Graft                         acid monomer  (parts)                                                                            BPO (parts)                                                                            MMA (parts)                                                                          nitride (parts)                                                                      (parts)                                                                             efficiency                    __________________________________________________________________________                                                    (%)                           Example 14                                                                          Methacrylic                                                                           10.0 1.0      30.0   270.0  720   92                                  acid                                                                    Example 15                                                                          Acrylic acid*1                                                                        7.6  1.0      30.0   270.0  720   94                            Example 16                                                                          Crotonic acid*2                                                                       10.0 1.0      30.0   270.0  720   92                            Example 17                                                                          Tiglic acid*3                                                                         11.4 1.0      30.0   270.0  720   71                            Example 18                                                                          Cinnamic                                                                              16.7 1.0      30.0   270.0  720   78                                  acid*4                                                                  Example 19                                                                          Maleic  11.0 1.0      30.0   270.0  720   90                                  anhydride*5                                                             __________________________________________________________________________     *1: CH.sub.2CHCO.sub.2 H                                                       *2: CH.sub.3 CHCHCO.sub.2 H                                                   *3: CH.sub.3 CHC(CH.sub.3)CO.sub.2 H                                          *4: C.sub.6 H.sub.5 CHCHCO.sub.2 H                                           ##STR8##                                                                 

As is apparent from Table 10, the graft efficiency was very high withmethacrylic acid, acrylic acid, crotonic acid and maleic anhydride.

EXAMPLES 20 to 30

The reaction was conducted in the same manner as in Example 14 exceptthat the type of the radical polymerization initiator was changed, andthe compositions thereby obtained were evaluated. The results are shownin Table 11.

                                      TABLE 11                                    __________________________________________________________________________    Radical         Carboxylic                                                                            Vinyl                                                                              Inorganic    Graft                               polymeri-       acid monomer                                                                          monomer                                                                            compound                                                                             Deionized                                                                           effi-                               zation     Amount                                                                             Methacrylic                                                                           MMA  Silicon                                                                              water ciency                              initiator  (parts)                                                                            acid (parts)                                                                          (Parts)                                                                            nitride (parts)                                                                      (parts)                                                                             (%)                                 __________________________________________________________________________    Example 14                                                                          BPO  1.0  10.0    30.0 270.0  720   92                                  Example 20                                                                          LPO *1                                                                             1.0  10.0    30.0 270.0  720   95                                  Example 21                                                                          AIBN *2                                                                            1.0  10.0    30.0 270.0  720   92                                  Example 22                                                                          AIBA *3                                                                            1.0  10.0    30.0 270.0  720   72                                  Example 23                                                                          KPS *4                                                                             1.0  10.0    30.0 270.0  720   75                                  __________________________________________________________________________     *1: Lauroyl peroxide                                                          *2: Azobisisobutyronitrile                                                    *3: 2,2'-Azobis(2aminodipropane)hydrochloride                                 *4: Potassium persulfate                                                 

As is apparent from Table 11, the graft efficiency was higher withlipophilic radical polymerization initiators such as BPO, LPO and AIBNthan with water-soluble AIBA and KPS.

EXAMPLES 24 and 25

The reaction was conducted in the same manner as in Example 14 exceptthat the vinyl monomer identified in Table 12 was used instead of methylmethacrylate as the vinyl monomer, and the compositions thereby obtainedwere evaluated. The results are shown in Table 12.

                                      TABLE 12                                    __________________________________________________________________________                    Carboxylic      Inorganic    Graft                                            acid monomer                                                                          Radical compound                                                                             Deionized                                                                           effi-                            Vinyl      Amount                                                                             Methacrylic                                                                           polymerization                                                                        Silicon                                                                              water ciency                           monomer    (parts)                                                                            acid (parts)                                                                          BPO (parts)                                                                           nitride (parts)                                                                      (parts)                                                                             (%)                              __________________________________________________________________________    Example 14                                                                          MMA  30.0 10.0    1.0     270.0  720   92                               Example 24                                                                          ST   30.0 10.0    1.0     270.0  720   78                               Example 25                                                                          AN   30.0 10.0    1.0     270.0  720   72                               __________________________________________________________________________     MMA: Methyl methacrylate, ST: Styrene, AN: Acrylonitrile                 

As is apparent from Table 12, according to the method of the presentinvention, a high graft efficiency can be attained with either one ofthe vinyl monomers (Examples 24 and 25). The applicability of a widerange of vinyl monomers is a feature of the present invention inaddition to the features of the high conversion and graft rate.

EXAMPLE 26

The reaction was conducted in the same manner as in Example 14 exceptthat the type of the inorganic compound was changed, and the compositionthereby obtained was evaluated. The results are shown in Table 13.

                                      TABLE 13                                    __________________________________________________________________________                     Carboxylic                                                                            Radical poly-                                                                        Vinyl      Graft                                               acid monomer                                                                          merization                                                                           monomer                                                                            Deionized                                                                           effi-                              Inorganic   Amount                                                                             Methacrylic                                                                           BPO    MMA  water ciency                             compound    (parts)                                                                            acid (parts)                                                                          (parts)                                                                              (parts)                                                                            (parts)                                                                             (%)                                __________________________________________________________________________    Example 1                                                                           Silicon                                                                             270.0                                                                              10.0    1.0    30.0 720   94                                       carbide                                                                 Example 2                                                                           Zirconium                                                                           270.0                                                                              10.0    1.0    30.0 720   95                                       oxide                                                                   Example 3                                                                           Zirconium                                                                           270.0                                                                              10.0    1.0    30.0 720   96                                       nitride                                                                 Example 4                                                                           Zirconium                                                                           270.0                                                                              10.0    1.0    30.0 720   93                                       boride                                                                  Example 5                                                                           Zirconium                                                                           270.0                                                                              10.0    1.0    30.0 720   92                                       carbide                                                                 __________________________________________________________________________

As is apparent from Table 13, the method of the present invention issuperior to the conventional non-catalytic polymerization system in boththe polymerization degree and the graft efficiency, and thus indicatesthat it is capable of providing a polymeric composition of a higherquality.

EXAMPLE 27 and COMPARATIVE EXAMPLES 15 to 18

As an evaluation of the applicability of the polymeric compositionobtained by the method of the present invention to a composite material,a combination of the polymeric composition with polymethyl methacrylateas matrix (inorganic compound content: 80 wt. %) was press-molded at200° C. under 20 kg/cm², and the molded product was evaluated for theouter appearance and bending strength. The results are shown in Table14.

                                      TABLE 14                                    __________________________________________________________________________                            Composite material                                                            composition *1                                                                           Outer                                                         Polymer                                                                            Polymeric  appearance                                                                          Bending                                     Polymeric   content                                                                            composition                                                                         PMMA of molded                                                                           strength                                    composition (%)  (parts)                                                                             (parts)                                                                            product                                                                             (kg/cm.sup.2)                        __________________________________________________________________________    Example 27                                                                           Example 14  9.7  88    12   ⊚                                                                    288                                         Present invention                                                      Comparative                                                                          Comparative Example 10                                                                    6.9  86    14   Δ                                                                             193                                  Example 15                                                                           Non-catalytic                                                                 polymerization                                                                system without                                                                addition of BPO                                                        Comparative                                                                          Comparative Example 11                                                                    1.1  81    19   X     72                                   Example 16                                                                           No addition of                                                                methacrylic acid as                                                           opposed to Example 14                                                  Comparative                                                                          Comparative Example 12                                                                    4.1  83    17   Δ                                                                             120                                  Example 17                                                                           Addition of                                                                   dispersant as opposed                                                         to Example 14                                                          Comparative                                                                          Non-treated silicon                                                                       --   80    20         64                                   Example 18                                                                           nitride                                                                __________________________________________________________________________     *1: The ratio of inorganic compound/organic compound = 80/20.                 PMMA: Polymethyl methacrylate, Acrypet (VH), manufactured by Mitsubishi       Rayon Co., Ltd.                                                               ⊚: Good,                                                       Δ: Fair,                                                                X: Poor,                                                                       : Bad                                                                   

As is apparent from Table 14, according to the method of the presentinvention (Example 27), a substantial improvement in the effects of thecombination is observed with respect to the outer appearance andstrength of the molded product.

We claim:
 1. A method for preparing a polymeric composition having aninorganic compound firmly consolidated thereonto, which comprisespolymerizing at least one radical polymerizable vinyl monomer using aperoxide or azo compound radical initiator in an aqueous polymerizationmedium, which medium comprises an inorganic compound dispersed in thepresence of an organic acid monomer or organic acid salt monomer,wherein said inorganic compound is selected from the group consisting ofa carbide, nitride and boride of silicon and zirconium, and zirconiumoxide; and wherein said organic acid monomer and organic acid saltmonomer is a carboxylic acid monomer or carboxylate monomer of theformula: ##STR9## wherein each of R₅ and R₆ is a hydrogen atom, a C₁-C₁₅ alkyl group or --COOA, wherein A is a hydrogen atom, an ammoniumradical or an alkali metal atom; R₇ is a hydrogen atom or a C₁ -C₁₅alkyl group; Z is a hydrogen atom, an ammonium radical or an alkalimetal atom; and each of R₈ and R₉ is a hydrogen atom or a C₁ -C₁₅ alkylgroup.
 2. The method according to claim 1, wherein the carboxylic acidmonomer is acrylic acid, methacrylic acid, crotonic acid, tiglic acid,cinnamic acid or maleic anhydride.
 3. The method according to claim 1,wherein the radical polymerization initiator is decomposable at atemperature within the range of from 40° to 100° C.